gcc/optabs-query.c

   1 /* IR-agnostic target query functions relating to optabs
   2    Copyright (C) 1987-2017 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "target.h"
  25 #include "insn-codes.h"
  26 #include "optabs-query.h"
  27 #include "optabs-libfuncs.h"
  28 #include "insn-config.h"
  29 #include "rtl.h"
  30 #include "recog.h"
  31
  32 struct target_optabs default_target_optabs;
  33 struct target_optabs *this_fn_optabs = &default_target_optabs;
  34 #if SWITCHABLE_TARGET
  35 struct target_optabs *this_target_optabs = &default_target_optabs;
  36 #endif
  37
  38 /* Return the insn used to perform conversion OP from mode FROM_MODE
  39    to mode TO_MODE; return CODE_FOR_nothing if the target does not have
  40    such an insn, or if it is unsuitable for optimization type OPT_TYPE.  */
  41
  42 insn_code
  43 convert_optab_handler (convert_optab optab, machine_mode to_mode,
  44                        machine_mode from_mode, optimization_type opt_type)
  45 {
  46   insn_code icode = convert_optab_handler (optab, to_mode, from_mode);
  47   if (icode == CODE_FOR_nothing
  48       || !targetm.optab_supported_p (optab, to_mode, from_mode, opt_type))
  49     return CODE_FOR_nothing;
  50   return icode;
  51 }
  52
  53 /* Return the insn used to implement mode MODE of OP; return
  54    CODE_FOR_nothing if the target does not have such an insn,
  55    or if it is unsuitable for optimization type OPT_TYPE.  */
  56
  57 insn_code
  58 direct_optab_handler (convert_optab optab, machine_mode mode,
  59                       optimization_type opt_type)
  60 {
  61   insn_code icode = direct_optab_handler (optab, mode);
  62   if (icode == CODE_FOR_nothing
  63       || !targetm.optab_supported_p (optab, mode, mode, opt_type))
  64     return CODE_FOR_nothing;
  65   return icode;
  66 }
  67
  68 /* Enumerates the possible types of structure operand to an
  69    extraction_insn.  */
  70 enum extraction_type { ET_unaligned_mem, ET_reg };
  71
  72 /* Check whether insv, extv or extzv pattern ICODE can be used for an
  73    insertion or extraction of type TYPE on a structure of mode MODE.
  74    Return true if so and fill in *INSN accordingly.  STRUCT_OP is the
  75    operand number of the structure (the first sign_extract or zero_extract
  76    operand) and FIELD_OP is the operand number of the field (the other
  77    side of the set from the sign_extract or zero_extract).  */
  78
  79 static bool
  80 get_traditional_extraction_insn (extraction_insn *insn,
  81                                  enum extraction_type type,
  82                                  machine_mode mode,
  83                                  enum insn_code icode,
  84                                  int struct_op, int field_op)
  85 {
  86   const struct insn_data_d *data = &insn_data[icode];
  87
  88   machine_mode struct_mode = data->operand[struct_op].mode;
  89   if (struct_mode == VOIDmode)
  90     struct_mode = word_mode;
  91   if (mode != struct_mode)
  92     return false;
  93
  94   machine_mode field_mode = data->operand[field_op].mode;
  95   if (field_mode == VOIDmode)
  96     field_mode = word_mode;
  97
  98   machine_mode pos_mode = data->operand[struct_op + 2].mode;
  99   if (pos_mode == VOIDmode)
 100     pos_mode = word_mode;
 101
 102   insn->icode = icode;
 103   insn->field_mode = field_mode;
 104   insn->struct_mode = (type == ET_unaligned_mem ? byte_mode : struct_mode);
 105   insn->pos_mode = pos_mode;
 106   return true;
 107 }
 108
 109 /* Return true if an optab exists to perform an insertion or extraction
 110    of type TYPE in mode MODE.  Describe the instruction in *INSN if so.
 111
 112    REG_OPTAB is the optab to use for register structures and
 113    MISALIGN_OPTAB is the optab to use for misaligned memory structures.
 114    POS_OP is the operand number of the bit position.  */
 115
 116 static bool
 117 get_optab_extraction_insn (struct extraction_insn *insn,
 118                            enum extraction_type type,
 119                            machine_mode mode, direct_optab reg_optab,
 120                            direct_optab misalign_optab, int pos_op)
 121 {
 122   direct_optab optab = (type == ET_unaligned_mem ? misalign_optab : reg_optab);
 123   enum insn_code icode = direct_optab_handler (optab, mode);
 124   if (icode == CODE_FOR_nothing)
 125     return false;
 126
 127   const struct insn_data_d *data = &insn_data[icode];
 128
 129   insn->icode = icode;
 130   insn->field_mode = mode;
 131   insn->struct_mode = (type == ET_unaligned_mem ? BLKmode : mode);
 132   insn->pos_mode = data->operand[pos_op].mode;
 133   if (insn->pos_mode == VOIDmode)
 134     insn->pos_mode = word_mode;
 135   return true;
 136 }
 137
 138 /* Return true if an instruction exists to perform an insertion or
 139    extraction (PATTERN says which) of type TYPE in mode MODE.
 140    Describe the instruction in *INSN if so.  */
 141
 142 static bool
 143 get_extraction_insn (extraction_insn *insn,
 144                      enum extraction_pattern pattern,
 145                      enum extraction_type type,
 146                      machine_mode mode)
 147 {
 148   switch (pattern)
 149     {
 150     case EP_insv:
 151       if (targetm.have_insv ()
 152           && get_traditional_extraction_insn (insn, type, mode,
 153                                               targetm.code_for_insv, 0, 3))
 154         return true;
 155       return get_optab_extraction_insn (insn, type, mode, insv_optab,
 156                                         insvmisalign_optab, 2);
 157
 158     case EP_extv:
 159       if (targetm.have_extv ()
 160           && get_traditional_extraction_insn (insn, type, mode,
 161                                               targetm.code_for_extv, 1, 0))
 162         return true;
 163       return get_optab_extraction_insn (insn, type, mode, extv_optab,
 164                                         extvmisalign_optab, 3);
 165
 166     case EP_extzv:
 167       if (targetm.have_extzv ()
 168           && get_traditional_extraction_insn (insn, type, mode,
 169                                               targetm.code_for_extzv, 1, 0))
 170         return true;
 171       return get_optab_extraction_insn (insn, type, mode, extzv_optab,
 172                                         extzvmisalign_optab, 3);
 173
 174     default:
 175       gcc_unreachable ();
 176     }
 177 }
 178
 179 /* Return true if an instruction exists to access a field of mode
 180    FIELDMODE in a structure that has STRUCT_BITS significant bits.
 181    Describe the "best" such instruction in *INSN if so.  PATTERN and
 182    TYPE describe the type of insertion or extraction we want to perform.
 183
 184    For an insertion, the number of significant structure bits includes
 185    all bits of the target.  For an extraction, it need only include the
 186    most significant bit of the field.  Larger widths are acceptable
 187    in both cases.  */
 188
 189 static bool
 190 get_best_extraction_insn (extraction_insn *insn,
 191                           enum extraction_pattern pattern,
 192                           enum extraction_type type,
 193                           unsigned HOST_WIDE_INT struct_bits,
 194                           machine_mode field_mode)
 195 {
 196   machine_mode mode = smallest_mode_for_size (struct_bits, MODE_INT);
 197   while (mode != VOIDmode)
 198     {
 199       if (get_extraction_insn (insn, pattern, type, mode))
 200         {
 201           while (mode != VOIDmode
 202                  && GET_MODE_SIZE (mode) <= GET_MODE_SIZE (field_mode)
 203                  && !TRULY_NOOP_TRUNCATION_MODES_P (insn->field_mode,
 204                                                     field_mode))
 205             {
 206               get_extraction_insn (insn, pattern, type, mode);
 207               mode = GET_MODE_WIDER_MODE (mode);
 208             }
 209           return true;
 210         }
 211       mode = GET_MODE_WIDER_MODE (mode);
 212     }
 213   return false;
 214 }
 215
 216 /* Return true if an instruction exists to access a field of mode
 217    FIELDMODE in a register structure that has STRUCT_BITS significant bits.
 218    Describe the "best" such instruction in *INSN if so.  PATTERN describes
 219    the type of insertion or extraction we want to perform.
 220
 221    For an insertion, the number of significant structure bits includes
 222    all bits of the target.  For an extraction, it need only include the
 223    most significant bit of the field.  Larger widths are acceptable
 224    in both cases.  */
 225
 226 bool
 227 get_best_reg_extraction_insn (extraction_insn *insn,
 228                               enum extraction_pattern pattern,
 229                               unsigned HOST_WIDE_INT struct_bits,
 230                               machine_mode field_mode)
 231 {
 232   return get_best_extraction_insn (insn, pattern, ET_reg, struct_bits,
 233                                    field_mode);
 234 }
 235
 236 /* Return true if an instruction exists to access a field of BITSIZE
 237    bits starting BITNUM bits into a memory structure.  Describe the
 238    "best" such instruction in *INSN if so.  PATTERN describes the type
 239    of insertion or extraction we want to perform and FIELDMODE is the
 240    natural mode of the extracted field.
 241
 242    The instructions considered here only access bytes that overlap
 243    the bitfield; they do not touch any surrounding bytes.  */
 244
 245 bool
 246 get_best_mem_extraction_insn (extraction_insn *insn,
 247                               enum extraction_pattern pattern,
 248                               HOST_WIDE_INT bitsize, HOST_WIDE_INT bitnum,
 249                               machine_mode field_mode)
 250 {
 251   unsigned HOST_WIDE_INT struct_bits = (bitnum % BITS_PER_UNIT
 252                                         + bitsize
 253                                         + BITS_PER_UNIT - 1);
 254   struct_bits -= struct_bits % BITS_PER_UNIT;
 255   return get_best_extraction_insn (insn, pattern, ET_unaligned_mem,
 256                                    struct_bits, field_mode);
 257 }
 258
 259 /* Return the insn code used to extend FROM_MODE to TO_MODE.
 260    UNSIGNEDP specifies zero-extension instead of sign-extension.  If
 261    no such operation exists, CODE_FOR_nothing will be returned.  */
 262
 263 enum insn_code
 264 can_extend_p (machine_mode to_mode, machine_mode from_mode,
 265               int unsignedp)
 266 {
 267   if (unsignedp < 0 && targetm.have_ptr_extend ())
 268     return targetm.code_for_ptr_extend;
 269
 270   convert_optab tab = unsignedp ? zext_optab : sext_optab;
 271   return convert_optab_handler (tab, to_mode, from_mode);
 272 }
 273
 274 /* Return the insn code to convert fixed-point mode FIXMODE to floating-point
 275    mode FLTMODE, or CODE_FOR_nothing if no such instruction exists.
 276    UNSIGNEDP specifies whether FIXMODE is unsigned.  */
 277
 278 enum insn_code
 279 can_float_p (machine_mode fltmode, machine_mode fixmode,
 280              int unsignedp)
 281 {
 282   convert_optab tab = unsignedp ? ufloat_optab : sfloat_optab;
 283   return convert_optab_handler (tab, fltmode, fixmode);
 284 }
 285
 286 /* Return the insn code to convert floating-point mode FLTMODE to fixed-point
 287    mode FIXMODE, or CODE_FOR_nothing if no such instruction exists.
 288    UNSIGNEDP specifies whether FIXMODE is unsigned.
 289
 290    On a successful return, set *TRUNCP_PTR to true if it is necessary to
 291    output an explicit FTRUNC before the instruction.  */
 292
 293 enum insn_code
 294 can_fix_p (machine_mode fixmode, machine_mode fltmode,
 295            int unsignedp, bool *truncp_ptr)
 296 {
 297   convert_optab tab;
 298   enum insn_code icode;
 299
 300   tab = unsignedp ? ufixtrunc_optab : sfixtrunc_optab;
 301   icode = convert_optab_handler (tab, fixmode, fltmode);
 302   if (icode != CODE_FOR_nothing)
 303     {
 304       *truncp_ptr = false;
 305       return icode;
 306     }
 307
 308   /* FIXME: This requires a port to define both FIX and FTRUNC pattern
 309      for this to work.  We need to rework the fix* and ftrunc* patterns
 310      and documentation.  */
 311   tab = unsignedp ? ufix_optab : sfix_optab;
 312   icode = convert_optab_handler (tab, fixmode, fltmode);
 313   if (icode != CODE_FOR_nothing
 314       && optab_handler (ftrunc_optab, fltmode) != CODE_FOR_nothing)
 315     {
 316       *truncp_ptr = true;
 317       return icode;
 318     }
 319
 320   return CODE_FOR_nothing;
 321 }
 322
 323 /* Return nonzero if a conditional move of mode MODE is supported.
 324
 325    This function is for combine so it can tell whether an insn that looks
 326    like a conditional move is actually supported by the hardware.  If we
 327    guess wrong we lose a bit on optimization, but that's it.  */
 328 /* ??? sparc64 supports conditionally moving integers values based on fp
 329    comparisons, and vice versa.  How do we handle them?  */
 330
 331 bool
 332 can_conditionally_move_p (machine_mode mode)
 333 {
 334   return direct_optab_handler (movcc_optab, mode) != CODE_FOR_nothing;
 335 }
 336
 337 /* Return true if VEC_PERM_EXPR of arbitrary input vectors can be
 338    expanded using SIMD extensions of the CPU.  SEL may be NULL, which
 339    stands for an unknown constant.  Note that additional permutations
 340    representing whole-vector shifts may also be handled via the vec_shr
 341    optab, but only where the second input vector is entirely constant
 342    zeroes; this case is not dealt with here.  */
 343
 344 bool
 345 can_vec_perm_p (machine_mode mode, bool variable,
 346                 const unsigned char *sel)
 347 {
 348   machine_mode qimode;
 349
 350   /* If the target doesn't implement a vector mode for the vector type,
 351      then no operations are supported.  */
 352   if (!VECTOR_MODE_P (mode))
 353     return false;
 354
 355   if (!variable)
 356     {
 357       if (direct_optab_handler (vec_perm_const_optab, mode) != CODE_FOR_nothing
 358           && (sel == NULL
 359               || targetm.vectorize.vec_perm_const_ok == NULL
 360               || targetm.vectorize.vec_perm_const_ok (mode, sel)))
 361         return true;
 362     }
 363
 364   if (direct_optab_handler (vec_perm_optab, mode) != CODE_FOR_nothing)
 365     return true;
 366
 367   /* We allow fallback to a QI vector mode, and adjust the mask.  */
 368   if (GET_MODE_INNER (mode) == QImode)
 369     return false;
 370   qimode = mode_for_vector (QImode, GET_MODE_SIZE (mode));
 371   if (!VECTOR_MODE_P (qimode))
 372     return false;
 373
 374   /* ??? For completeness, we ought to check the QImode version of
 375       vec_perm_const_optab.  But all users of this implicit lowering
 376       feature implement the variable vec_perm_optab.  */
 377   if (direct_optab_handler (vec_perm_optab, qimode) == CODE_FOR_nothing)
 378     return false;
 379
 380   /* In order to support the lowering of variable permutations,
 381      we need to support shifts and adds.  */
 382   if (variable)
 383     {
 384       if (GET_MODE_UNIT_SIZE (mode) > 2
 385           && optab_handler (ashl_optab, mode) == CODE_FOR_nothing
 386           && optab_handler (vashl_optab, mode) == CODE_FOR_nothing)
 387         return false;
 388       if (optab_handler (add_optab, qimode) == CODE_FOR_nothing)
 389         return false;
 390     }
 391
 392   return true;
 393 }
 394
 395 /* Like optab_handler, but for widening_operations that have a
 396    TO_MODE and a FROM_MODE.  */
 397
 398 enum insn_code
 399 widening_optab_handler (optab op, machine_mode to_mode,
 400                         machine_mode from_mode)
 401 {
 402   unsigned scode = (op << 16) | to_mode;
 403   if (to_mode != from_mode && from_mode != VOIDmode)
 404     {
 405       /* ??? Why does find_widening_optab_handler_and_mode attempt to
 406          widen things that can't be widened?  E.g. add_optab... */
 407       if (op > LAST_CONV_OPTAB)
 408         return CODE_FOR_nothing;
 409       scode |= from_mode << 8;
 410     }
 411   return raw_optab_handler (scode);
 412 }
 413
 414 /* Find a widening optab even if it doesn't widen as much as we want.
 415    E.g. if from_mode is HImode, and to_mode is DImode, and there is no
 416    direct HI->SI insn, then return SI->DI, if that exists.
 417    If PERMIT_NON_WIDENING is non-zero then this can be used with
 418    non-widening optabs also.  */
 419
 420 enum insn_code
 421 find_widening_optab_handler_and_mode (optab op, machine_mode to_mode,
 422                                       machine_mode from_mode,
 423                                       int permit_non_widening,
 424                                       machine_mode *found_mode)
 425 {
 426   for (; (permit_non_widening || from_mode != to_mode)
 427          && GET_MODE_SIZE (from_mode) <= GET_MODE_SIZE (to_mode)
 428          && from_mode != VOIDmode;
 429        from_mode = GET_MODE_WIDER_MODE (from_mode))
 430     {
 431       enum insn_code handler = widening_optab_handler (op, to_mode,
 432                                                        from_mode);
 433
 434       if (handler != CODE_FOR_nothing)
 435         {
 436           if (found_mode)
 437             *found_mode = from_mode;
 438           return handler;
 439         }
 440     }
 441
 442   return CODE_FOR_nothing;
 443 }
 444
 445 /* Return non-zero if a highpart multiply is supported of can be synthisized.
 446    For the benefit of expand_mult_highpart, the return value is 1 for direct,
 447    2 for even/odd widening, and 3 for hi/lo widening.  */
 448
 449 int
 450 can_mult_highpart_p (machine_mode mode, bool uns_p)
 451 {
 452   optab op;
 453   unsigned char *sel;
 454   unsigned i, nunits;
 455
 456   op = uns_p ? umul_highpart_optab : smul_highpart_optab;
 457   if (optab_handler (op, mode) != CODE_FOR_nothing)
 458     return 1;
 459
 460   /* If the mode is an integral vector, synth from widening operations.  */
 461   if (GET_MODE_CLASS (mode) != MODE_VECTOR_INT)
 462     return 0;
 463
 464   nunits = GET_MODE_NUNITS (mode);
 465   sel = XALLOCAVEC (unsigned char, nunits);
 466
 467   op = uns_p ? vec_widen_umult_even_optab : vec_widen_smult_even_optab;
 468   if (optab_handler (op, mode) != CODE_FOR_nothing)
 469     {
 470       op = uns_p ? vec_widen_umult_odd_optab : vec_widen_smult_odd_optab;
 471       if (optab_handler (op, mode) != CODE_FOR_nothing)
 472         {
 473           for (i = 0; i < nunits; ++i)
 474             sel[i] = !BYTES_BIG_ENDIAN + (i & ~1) + ((i & 1) ? nunits : 0);
 475           if (can_vec_perm_p (mode, false, sel))
 476             return 2;
 477         }
 478     }
 479
 480   op = uns_p ? vec_widen_umult_hi_optab : vec_widen_smult_hi_optab;
 481   if (optab_handler (op, mode) != CODE_FOR_nothing)
 482     {
 483       op = uns_p ? vec_widen_umult_lo_optab : vec_widen_smult_lo_optab;
 484       if (optab_handler (op, mode) != CODE_FOR_nothing)
 485         {
 486           for (i = 0; i < nunits; ++i)
 487             sel[i] = 2 * i + (BYTES_BIG_ENDIAN ? 0 : 1);
 488           if (can_vec_perm_p (mode, false, sel))
 489             return 3;
 490         }
 491     }
 492
 493   return 0;
 494 }
 495
 496 /* Return true if target supports vector masked load/store for mode.  */
 497
 498 bool
 499 can_vec_mask_load_store_p (machine_mode mode,
 500                            machine_mode mask_mode,
 501                            bool is_load)
 502 {
 503   optab op = is_load ? maskload_optab : maskstore_optab;
 504   machine_mode vmode;
 505   unsigned int vector_sizes;
 506
 507   /* If mode is vector mode, check it directly.  */
 508   if (VECTOR_MODE_P (mode))
 509     return convert_optab_handler (op, mode, mask_mode) != CODE_FOR_nothing;
 510
 511   /* Otherwise, return true if there is some vector mode with
 512      the mask load/store supported.  */
 513
 514   /* See if there is any chance the mask load or store might be
 515      vectorized.  If not, punt.  */
 516   vmode = targetm.vectorize.preferred_simd_mode (mode);
 517   if (!VECTOR_MODE_P (vmode))
 518     return false;
 519
 520   mask_mode = targetm.vectorize.get_mask_mode (GET_MODE_NUNITS (vmode),
 521                                                GET_MODE_SIZE (vmode));
 522   if (mask_mode == VOIDmode)
 523     return false;
 524
 525   if (convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
 526     return true;
 527
 528   vector_sizes = targetm.vectorize.autovectorize_vector_sizes ();
 529   while (vector_sizes != 0)
 530     {
 531       unsigned int cur = 1 << floor_log2 (vector_sizes);
 532       vector_sizes &= ~cur;
 533       if (cur <= GET_MODE_SIZE (mode))
 534         continue;
 535       vmode = mode_for_vector (mode, cur / GET_MODE_SIZE (mode));
 536       mask_mode = targetm.vectorize.get_mask_mode (GET_MODE_NUNITS (vmode),
 537                                                    cur);
 538       if (VECTOR_MODE_P (vmode)
 539           && convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
 540         return true;
 541     }
 542   return false;
 543 }
 544
 545 /* Return true if there is a compare_and_swap pattern.  */
 546
 547 bool
 548 can_compare_and_swap_p (machine_mode mode, bool allow_libcall)
 549 {
 550   enum insn_code icode;
 551
 552   /* Check for __atomic_compare_and_swap.  */
 553   icode = direct_optab_handler (atomic_compare_and_swap_optab, mode);
 554   if (icode != CODE_FOR_nothing)
 555     return true;
 556
 557   /* Check for __sync_compare_and_swap.  */
 558   icode = optab_handler (sync_compare_and_swap_optab, mode);
 559   if (icode != CODE_FOR_nothing)
 560     return true;
 561   if (allow_libcall && optab_libfunc (sync_compare_and_swap_optab, mode))
 562     return true;
 563
 564   /* No inline compare and swap.  */
 565   return false;
 566 }
 567
 568 /* Return true if an atomic exchange can be performed.  */
 569
 570 bool
 571 can_atomic_exchange_p (machine_mode mode, bool allow_libcall)
 572 {
 573   enum insn_code icode;
 574
 575   /* Check for __atomic_exchange.  */
 576   icode = direct_optab_handler (atomic_exchange_optab, mode);
 577   if (icode != CODE_FOR_nothing)
 578     return true;
 579
 580   /* Don't check __sync_test_and_set, as on some platforms that
 581      has reduced functionality.  Targets that really do support
 582      a proper exchange should simply be updated to the __atomics.  */
 583
 584   return can_compare_and_swap_p (mode, allow_libcall);
 585 }
 586
 587 /* Return true if an atomic load can be performed without falling back to
 588    a compare-and-swap.  */
 589
 590 bool
 591 can_atomic_load_p (machine_mode mode)
 592 {
 593   enum insn_code icode;
 594
 595   /* Does the target supports the load directly?  */
 596   icode = direct_optab_handler (atomic_load_optab, mode);
 597   if (icode != CODE_FOR_nothing)
 598     return true;
 599
 600   /* If the size of the object is greater than word size on this target,
 601      then we assume that a load will not be atomic.  Also see
 602      expand_atomic_load.  */
 603   return GET_MODE_PRECISION (mode) <= BITS_PER_WORD;
 604 }
 605
 606 /* Determine whether "1 << x" is relatively cheap in word_mode.  */
 607
 608 bool
 609 lshift_cheap_p (bool speed_p)
 610 {
 611   /* FIXME: This should be made target dependent via this "this_target"
 612      mechanism, similar to e.g. can_copy_init_p in gcse.c.  */
 613   static bool init[2] = { false, false };
 614   static bool cheap[2] = { true, true };
 615
 616   /* If the targer has no lshift in word_mode, the operation will most
 617      probably not be cheap.  ??? Does GCC even work for such targets?  */
 618   if (optab_handler (ashl_optab, word_mode) == CODE_FOR_nothing)
 619     return false;
 620
 621   if (!init[speed_p])
 622     {
 623       rtx reg = gen_raw_REG (word_mode, 10000);
 624       int cost = set_src_cost (gen_rtx_ASHIFT (word_mode, const1_rtx, reg),
 625                                word_mode, speed_p);
 626       cheap[speed_p] = cost < COSTS_N_INSNS (3);
 627       init[speed_p] = true;
 628     }
 629
 630   return cheap[speed_p];
 631 }